1. Field of the Invention
The present invention relates to a mounting device of a code plate which is used to detect focal length data or the like, for example in a zoom lens camera
2. Description of the Related Art
In a conventional photographing lens, such as a zoom lens, a two-focus lens, or a macro lens, etc., a cam ring is either manually or automatically rotated by a motor to move a group of variable power lenses provided in the cam ring in the optical axis direction, so that the variable power lenses move away from and towards each other to change the focal length thereof or the like. In a camera having such a photographing lens, lens information (data), such as the varied focal length or the open F-number, which varies in accordance with the focal length, are automatically detected to effect the operation of the camera.
A code plate which is provided on the outer periphery of the cam ring and which is selectively brought into contact with brushes has been used as an automatic detecting means for detecting the lens data which has been used. This has been done so that the position of the contact of the brushes with the code plate is read as position data. The position data thus read is converted to focal length data, etc. The code plate is usually attached to the cam ring with an adhesive tape or by set screws. In this attaching mechanism, the precision of the detection of the position data largely depends on the precision of the attachment of the code plate.
However, it is very difficult to precisely attach the code plate to the outer cylindrical periphery of the cam ring with adhesive tape. Furthermore, an undesirable displacement of the code plate on the cam ring tends to occur during the attachment, which is in any case a troublesome operation. If the code plate is reattached to the cam ring, for example, after a failure to attachment, the code plate tends to detach from the cam ring because of a decrease in the adhesive force, due to aging.
On the other hand, in the case of the attachment of the code plate using set screws, there is no (or a lesser) possibility of detachment due to aging. However, the engagement of the set screws in corresponding small threaded holes is a troublesome and time-consuming operation, thus resulting in decreased efficiency of assembly.